If you're still interested in this mod, might I suggest some new features such as adding tool speed, so the crook is affected by tool-speed settings like the axes are. Also adding new crooks, with higher chances to produce saplings, or to break multiple leaves like shears perhaps? I just like the ridiculous idea of a diamond encrusted steel crook that can break a 3x3 of leaves for 2-3 saplings per leaf.
More seriously, a bone crook to use those stacks of bones I keep ending up with would be nice, maybe decorated with feathers to increase the use speed? Actually, being able to decorate any crook with feathers to increase its use speed would be nice, since they have no use (save for arrows that I hardly ever use) that I know of.